In the process of producing a semiconductor device such as IC and LSI, microfabrication by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using electron beam, X-ray or EUV light is also proceeding.
The lithography using electron beam, X-ray or EUV light is positioned as a next-generation or next-next-generation pattern formation technique and a high-sensitivity and high-resolution resist is being demanded.
Particularly, in order to shorten the wafer processing time, the elevation of sensitivity is very important, but when higher sensitivity is sought for, this incurs not only reduction in the resolution but also worsening of the line width roughness, and development of a resist satisfying all of these properties at the same time is strongly demanded.
The line width roughness as used herein means that the resist edge at the interface between the pattern and the substrate irregularly fluctuates in the direction perpendicular to the line direction due to resist characteristics and when the pattern is viewed from right above, the edge gives an uneven appearance. This unevenness is transferred in the etching step using the resist as a mask and gives rise to deterioration of electrical properties and in turn, reduction in the yield.
The high sensitivity is in a trade-off relationship with high resolution, good pattern profile and good line width roughness, and it is very important how to satisfy all of these properties at the same time.
The resist composition includes “a positive type” using a resin sparingly-soluble or insoluble in an alkali developer, where the exposed area is solubilized by an alkali developer at the exposure to radiation and a pattern is thereby formed, and “a negative type” using a resin soluble in an alkali developer, where the exposed area is sparingly solubilized or insolubilized by an alkali developer at the exposure to radiation and a pattern is thereby formed.
As regards the resist suitable for such a lithography process using electron beam, X-ray or EUV light, a chemical amplification positive resist utilizing an acid catalytic reaction is mainly studied from the standpoint of elevating the sensitivity, and a chemical amplification positive resist composition containing, as main components, an acid generator and a phenolic resin having a property of being insoluble or sparingly soluble in an alkali developer but becoming soluble in an alkali developer by the action of an acid (hereinafter simply referred to as a “phenolic acid-decomposable resin”) is being effectively used.
In the production of a semiconductor device or the like, various patterns such as line, trench and hole need to be fowled. For meeting the requirement to form various patterns, not only a positive resist composition but also a negative resist composition are currently under development. For example, JP-A-2002-148806 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-2008-268935 disclose a negative chemical-amplification resist composition for electron beam or X-ray lithography and a technique of forming a pattern by subjecting a film formed from the composition to exposure and then development using an alkali developer.
In the formation of an ultrafine pattern, it is demanded to more improve the reduction of resolution and the line width roughness.
With an attempt to satisfy this demand, there has been also proposed a method where a film formed from a resist composition containing an acid-decomposable resin is exposed and then developed using a developer other than an alkali developer. For example, Japanese Patent No. 3277114 discloses developing the film with a supercritical fluid (supercritical CO2), and JP-A-7-199467 discloses a method where a film formed from a resist composition containing a resin having a group capable of being cleaved by the action of an acid to cause polarity conversion (deprotection reaction) is exposed and then developed with a developer containing an organic solvent.
Furthermore, a pattern forming method using a resin whose main chain is cut directly by exposure is also known. For example, JP-A-62-175739 and JP-A-2006-227174 disclose a non-chemical amplification positive resist composition containing a copolymer of PMMA (polymethyl methacrylate) or methyl α-chloroacrylate with α-methylstyrene. According to such a method, the chain of the polymer is cut upon irradiation with radiation such as electron beam to decrease the molecular weight and in turn, the dissolution rate in an organic solvent as a developer is increased, whereby a pattern is formed.
However, it is impossible at present to satisfy high sensitivity, high resolution, good pattern profile and good line width roughness in the ultrafine region all at the same time.